In recent years, light-emitting diode (LED) technologies have improved a lot, and LEDs with high power and high brightness have been presented to the market. In addition, the LEDs used as light bulbs have the advantage of long lifetime. Therefore, such LED light bulbs have the tendency to replace other conventional light sources. LEDs can be applied to various types of lamps, such as traffic lights, street lights, and flashlights.
Since LEDs gradually become mainstream light sources, improving properties of LEDs becomes an important issue, and this becomes the main goal in the R&D departments of the LED industries.